Find the Exact Value Of $\operatorname { sit } \left( \frac { 9 x } { 2 } \right)$

Short Answer

Find the exact value of $\operatorname { sit } \left( \frac { 9 x } { 2 } \right)$ and $\operatorname { Cos} \left( - \frac { 9 x } { 2 } \right)$ .